A quasi-three-dimensional large-signal dynamic model of distributed feedback lasers

A simple, but powerful, quasi-three-dimensional large-signal dynamic model of distributed feedback semiconductor laser is presented. The transient response of lasers is analyzed by using a combined beam propagation method and time-domain algorithm that is capable of including the longitudinal and lateral variation of the optical-mode and carrier density profiles. In addition, the spontaneous emission noise, the nonuniform current injection resulting from the variation of Fermi-voltage as well as that of the refractive index distribution are also taken into consideration. Using this model, the influence of nonuniform waveguide structure on the static and dynamic responses of distributed feedback lasers is analyzed. In addition, a novel double tapered waveguide distributed feedback laser is proposed for stable single-mode operation at high power.published_or_final_versio

Nonlinear dynamics of vertical-cavity surface-emitting lasers

The dependence of the transient response of a vertical-cavity surface-emitting laser (VCSEL) on its aperture size is investigated subject to direct current modulation and external optical feedback. It is shown that lasers with small aperture size suppress higher order bifurcations and chaos even under large-signal modulation and external optical feedback. Furthermore, the noise characteristics of VCSELs under the influence of external optical feedback are studied via the calculation of relative intensity noise. It is found that the level of external optical feedback for the onset of coherence collapse is high for devices with small aperture size. On the other hand, the small-signal response of lasers is also analyzed through the calculation of third-order harmonic distortion. It is shown that harmonic distortion is minimized in small devices. Therefore, VCSELs with small aperture size have better immunity to irregular response under direct current modulation and external optical feedback.published_or_final_versio

Dynamic behavior of vertical-cavity surface-emitting lasers

A quasi-three-dimensional dynamic model of index-guided vertical-cavity surface-emitting lasers is developed. Detailed structure of Bragg reflectors and lateral optical confinement are considered into the model. A three-dimensional waveguide problem is reduced to one dimension by using the effective-index method. The dynamic response of optical field is solved by the time-domain algorithm. In addition, the lateral variation of carrier concentration, refractive index, and spontaneous-emission profile are also determined in a self consistent manner. Using this model, the influence of carrier transport and hot carriers on the dynamic behavior of vertical-cavity surface emitting lasers is studied. It is found that these nonlinearities have significant influence on the relaxation-oscillation frequency and modulation bandwidth of the devices.published_or_final_versio

Theoretical analysis of polarization bistability in vertical cavity surface emitting semiconductor lasers

The polarization bistability of vertical cavity surface emitting lasers under external optical injection is analyzed theoretically. It is found that on the condition where the optical gain is blue-shifted relative to the cavity mode, the bistable characteristics of VCSEL's can be improved significantly: (1) low optical power of the external injection light is required, (2) the influence of self-heating effects is minimized, and (3) wide bistable hysteresis loop width can be maintained. Furthermore, it is also shown that the reflectivity of Bragg reflectors should also be optimized to improve the performance of VCSEL's as bistable switches.published_or_final_versio

Polarization bistability of vertical cavity lasers under external optical injection

The polarization bistability of VCLs is studied theoretically with the consideration of dielectric Bragg reflectors, surface coatings, carrier induced refractive index inside the active layer as well as the intensity and wavelength of the injected light. The VCL has a built-in index guided structure and a GaAs-Al0.3Ga0.7As quantum well active layer. A rate-equation model is developed. It is shown that all-optical switching and memory operation can be achieved in VCLs by external optical injection, however, devices with suitable design of surface coating and Bragg reflectors are required.published_or_final_versio

An improved time-domain traveling-wave model for vertical-cavity surface-emitting lasers

The use of the time-dependent transfer matrix and wide-angle beam propagation method is proposed to improve the computational speed and accuracy of a recently developed time-domain traveling-wave model of vertical-cavity surface-emitting lasers. With suitable utilization of the transfer matrix, significant reduction of the total execution time of the traveling-wave model can be obtained. In addition, the use of the wide-angle beam propagation method can minimize the calculation error of the traveling-wave model due to the diffraction of light from the small aperture of the laser cavity.published_or_final_versio

Double-tapered-waveguide distributed feedback lasers for high-power single-mode operation

Theoretical analysis of double-tapered-waveguide distributed feedback semiconductor laser for stable single-mode and high-power operation is presented. It is found that the single-mode behavior of a distributed feedback laser with large coupling-length product can be improved significantly by the double-tapered-waveguide structure.published_or_final_versio

Analysis and design of vertical-cavity surface-emitting lasers for self-sustained pulsation operation

The generation mechanism of self-sustained pulsation in vertical-cavity surface-emitting lasers (VCSELs) is analyzed with the influence of lateral loss effects, such as self-focusing, lateral diffraction loss, and spatial hole burning, taken into consideration. The condition for self-sustained pulsation is also derived in an analytical form. It is shown that the lateral loss effects have significant influence on the excitation of self-sustained pulsation, especially for devices with small size. Furthermore, the possibility of using diffused quantum-well (QW) structures in VCSELs to enhance self-sustained pulsation is studied. It is found that by using diffused QW structures, the range of core area to obtain self-sustained pulsation is increased. In addition, peak power and repetition frequency of the pulses can also be improved.published_or_final_versio

Dynamic behavior of double-tapered-waveguide distributed feedback lasers

Dynamic behavior of a double-tapered-waveguide (DTWG) distributed feedback (DFB) semiconductor laser is analyzed theoretically. It is found that the relaxation oscillation frequency can he enhanced by the DTWG structure especially for DFB lasers with large coupling-length product.published_or_final_versio

Proposed enhancement of side-mode suppression ratio in λ/4 shifted distributed feedback lasers with nonuniform diffused quantum wells

An enhancement of the side mode suppression ratio, by utilizing interdiffused quantum wells, of a λ/4 shifted distributed feedback laser is demonstrated theoretically. It is found that by introducing a diffusion step along the longitudinal direction of the quantum-well active region, the suppression ratio can be improved significantly for large /spl kappa/L (>2.6) devices. The maximum power for single longitudinal mode operation is increased by more than 50 mW.published_or_final_versio